Agitation apparatus

ABSTRACT

An agitation apparatus which is suitable for use in a cleaning head of a vacuum cleaner includes first and second flow paths. Each of these flow paths has a resonant cavity and an inlet/outlet port which joins the cavity to a space within the cleaning head. A generating means or generator, such as a loudspeaker with a diaphragm, generates an alternating pressure wave between the ports. Pressure waves are emitted from one of the ports in an anti-phase relationship with the pressure waves from the other of the ports, thus reducing operating noise. Due to both sides of the generator or diaphragm being exposed to an equal static pressure, the generator operates more reliably. A plurality of these arrangements can be provided across the cleaning head, and a part of the agitation apparatus, such as the driver, can be mounted on the main body of the vacuum cleaner.

This invention relates to an agitation apparatus which is particularlysuitable for, but not limited to, use with a cleaning appliance such asa vacuum cleaner.

Vacuum cleaners generally remove dirt, dust and other debris from asurface by a combination of a suction force, generated by a motor-drivenfan, and some form of mechanical agitation of the floor surface. Themechanical agitation often takes the form of a rotating brush bar whichis driven by a motor or by an air turbine. The rotating brush bar‘beats’ the carpet pile while the suction force ‘sucks’ dirt and dustfrom the surface.

Agitation of a carpet by a brush bar inevitably causes some damage tothe carpet and also causes wear on the brush bar and the drive systemfor the brush bar.

There have been various proposals for tools which make use of avibrating airstream to promote the release of dirt from a carpet. U.S.Pat. No. 5,400,466 shows a cleaning head with a loudspeaker supportedand sealed within the cleaning head which directs airwaves towards thesurface in the frequency range of 10-200 Hz or 200-500 Hz.

However, tools of this kind have a disadvantage in that they can benoisy in use. Also, the use of a loudspeaker near to a source of suctioncauses problems with operation of the loudspeaker since there is atendency for the loudspeaker cone to be sucked towards the source ofsuction.

The present invention seeks to provide an improved way of agitating asurface or other medium which requires agitation.

Accordingly, a first aspect of the present invention provides anagitation apparatus according to claim 1.

This agitation system has an advantage in that pressure waves areemitted from a first of the ports in anti-phase with the pressure wavesfrom the second of the ports. At a normal operating distance from theapparatus (the so-called far-field), a user will hear little or no noisefrom the apparatus since the pressure waves cancel one another. Althoughthere is little or no noise, there is still a net flow of air betweenthe ports which can agitate something placed beneath the ports. Thegenerating means functions as a kind of air pump, acting on the volumeof air in the flow paths.

The agitation apparatus is particularly suitable for use with, or aspart of, a cleaning appliance such as a vacuum cleaner. Accordingly,further aspects of the invention provide a cleaning head, a vacuumcleaner and an agitation apparatus for use with a vacuum cleaner. Theports of the agitation apparatus can form part of a cleaning head of thecleaning appliance. The agitation apparatus is particularly suitable foruse as part of a suction head of a vacuum cleaner since any materialwhich is dislodged by the pressure waves can be carried away by the mainsuction flow through the suction head. A further advantage when thisarrangement is used as part of a vacuum cleaner is that, since the twosides of the generating means (diaphragm) are exposed to an equal staticpressure, the diaphragm will not be sucked towards the source of suctionon the cleaner. However, it will be appreciated that the applications ofthis apparatus extend beyond cleaning appliances.

The absence of mechanical contact with the surface can help to reducewear on the surface. Rather than mechanically agitating the carpet, theair motion vibrates the pile of the carpet, drawing out dust from thecarpet pile. This dust can be extracted along with the bulk air flow.Preferably, the frequency of the generating means is equal to, or closeto, the resonant frequency of the carpet pile. This can help to ‘boil’dirt upwards from the base of the carpet pile towards the surface.Preferably the frequency of operation of the generating means ismanually adjustable, or automatically adjustable according to the typeof carpet or surface beneath the cleaning head.

In its simplest form, each flow path is a cavity with a port extendingdirectly from it. The generating means can act directly on the cavity.In a more elaborate scheme, the flow path can comprise further ductingwhich connects the main, resonating, cavity to the generating means.This scheme can be of use in applications where it is undesirable, orimpossible, to house the generating means adjacent to where theagitation is required. As an example, in a vacuum cleaner it isundesirable to increase the size and weight of the cleaner head. Thus,the generating means can be positioned on the main body of the vacuumcleaner with ducting connecting the generating means to the resonatingcavity on the cleaner head.

Each cavity can have a single port or a plurality of ports. The shape ofthe ports can be adapted to the application. A rectangular cross-sectionhas been found to work well when the agitation apparatus forms part of acleaning head.

Preferably the generating means comprises a diaphragm. The term‘diaphragm’ is intended to be construed broadly, to encompass a broadrange of movable members. The diaphragm can be either a flexible memberor a rigid member which is flexibly mounted to the walls of thecompartment. Where a single diaphragm is used, a first side of thediaphragm communicates with the first flow path and a second side of thediaphragm communicates with the second flow path so that the two sidesof the diaphragm generate the first and second alternating pressurewaves. A driver for driving the diaphragm can be housed within one ofthe flow paths (or cavities), or there can be two drivers, one on eachside of the diaphragm.

Where two diaphragms are used, these can be spaced apart from oneanother with a driver mounted between them. Preferably the diaphragmsare driven in unison so that one flow path (or cavity) is compressed asanother is rarefied.

Preferably the first and second cavities are of substantially the samevolume. The more symmetrical the system is made, the better matched thetwo pressure waves will be, and thus the better the two pressure waveswill cancel one another. Preferably the cavities are tuned for thefrequency at which the generating means operates, as this maximises thequality factor (Q) of the apparatus. We have also found that it ispreferable for the ports to be tuned at a frequency which is greaterthan (such as twice) the frequency of operation of the generating meansas this maximises air movement through the ports.

The generating means can be in the form of a loudspeaker. It is possiblefor the coil, or the magnet, to be mounted to, and movable with, thediaphragm while the other of the magnet or coil remains stationary. Aloudspeaker type of driver has an advantage in that it is cheaper andproduces lower noise in operation compared to a piston type of driver,since there is no direct connection to the diaphragm. Other forms of thegenerating means include a cam or a piston which acts on the diaphragmor diaphragms, the cam or piston being driven by a motor or by airflowthrough the appliance. The coil of the loudspeaker can be directlydriven by a signal at mains frequency or from a signal derived from asignal source.

For an agitation apparatus which is part of a cleaning head for use withfloor surfaces, it has been found that best results are obtained withthe generating means generating a pressure wave with a frequency in therange 0-200 Hz.

Preferably the ports are arranged so that they are directed downwardlytowards a surface and inclined towards one another.

A cleaning head can incorporate a plurality of the agitation apparatus.

Embodiments of the invention will now be described with reference to thedrawings, in which:

FIGS. 1A and 1B show a conventional upright type of vacuum cleaner inwhich the agitation apparatus can be used;

FIG. 2 shows a cleaning head incorporating the agitation apparatus;

FIG. 3 shows the agitation apparatus in more detail;

FIG. 4 shows a single one of the cavities used in the agitationapparatus;

FIG. 5 shows the positioning of the ports on the agitation apparatus;

FIG. 6 shows a first way of driving the generating means;

FIG. 7 shows a second way of driving the generating means;

FIG. 8 shows a way of automatically adjusting the frequency of operationof the generating means;

FIG. 9 shows a symmetrical driver arrangement for the agitationapparatus;

FIG. 10 shows another driver arrangement for the agitation apparatus;

FIGS. 11 to 13 show arrangements where a part of the agitation apparatusis positioned away from the cleaning head;

FIG. 14 shows a way of mounting a plurality of the agitation apparatusin a cleaning head;

FIG. 15 shows another way of arranging a plurality of the agitationapparatus;

FIG. 16 shows an agitation apparatus which has an alternative form ofgenerating means;

FIG. 17 shows a cleaning head for use with a cylinder type of vacuumcleaner;

FIG. 18 shows an alternative form of the agitation apparatus.

Before describing the cleaning head in detail, FIGS. 1A and 1B show anexample of an upright type of vacuum cleaner in which the cleaning headcan be used. Dirty air can be drawn into the cleaner via a cleaner head12, if on-the-floor cleaning is required, or via a hose and wandassembly 11, if above-the-floor or manual cleaning is required. Dirtyair is drawn into the cleaner along path A. The dirty air is carriedalong path C before entering a separating apparatus 15 which serves toseparate dirt and dust from the dirty air (path D) as well as collectthe separated material. The separating apparatus can be a cyclonicseparator, as shown here, or some other form of separator, such as afilter bag. Cleaned air leaves the separator along paths E, F beforeentering (G) a fan and motor housing 20 at the base of the cleaner. Thefan and motor housing 20 supports a fan and a motor to drive the fan. Inuse, the motor 25 rotates the fan to draw air along the paths A-Hthrough the cleaner. Air is exhausted from the cleaner (path H) via asuitable outlet.

A cleaning head 12 for use in this vacuum cleaner is shown incross-section in FIG. 2. The casing 50 of the cleaning head 12 defines asuction housing. The lower, floor facing side 53 of the suction housingis a sole plate which can ride along the floor surface. Small rollersmay also be provided on the base of the sole plate to allow the cleaninghead to roll across hard floor surfaces. A suction opening 54 is definedin the sole plate 53. In use, the floor covering (such as a carpet)projects through the suction opening 54. A suction outlet 130 connectsthe suction housing 50 to the separating apparatus and fan and motor onthe main body of the vacuum cleaner, as previously described. Thesefeatures are all well known in conventional cleaning heads.

Mounted on the upper face of the cleaning head 12 is the agitationsystem. In its simplest form, this comprises a housing 100 which isdivided into two compartments, or cavities, 101, 102. For each cavity101, 102, a tube-like port 110, 120 extends from the inside of thecavity 101, 102 into the suction housing 55. The two cavities 101, 102are separated by a dividing wall 201. A diaphragm 206 of a driver 200 ismounted in an aperture in the dividing wall 201 and sealed against thewall 201, as better shown in FIG. 3. In this embodiment the driver 200is schematically shown in the form of a loudspeaker. Each side of thediaphragm 206 communicates with a respective one of the cavities, 101,102 i.e. a first side of the diaphragm 206 communicates with cavity 101and a second side of the diaphragm 206 communicates with cavity 102. Theouter edge of the diaphragm 206 is connected to the dividing wall 201 bya flexible seal 204 which allows the diaphragm 206 to move, in use, butmaintains an airtight seal between the cavities 101, 102. This seal 204extends around the entire perimeter of the diaphragm 206. The diaphragm206 is driven by a magnet 210 and coil 215 combination which in turn isdriven by an ac source. This will be described in more detail below. Theac frequencies can be in the range of 0 to 200 Hz. The driver 200 servesto move air backwards and forwards between the ports 110, 120 and acrossthe carpet pile, or other floor covering, which projects into thesuction inlet 54 of the cleaning head.

Each cavity 101, 102 has a volume V which is driven by the diaphragm 206at the chosen frequency. The driver 200 compresses the air in thecavity, the compressed air venting through the port 110. When the driverchanges direction, the air motion also changes direction. The phaserelationship between movement of the diaphragm 206 and movement of airthrough the ports 110, 120 varies according to the frequency ofoperation. At low frequencies, the movement of the diaphragm 206 isgenerally in phase with movement of air from the port, e.g. as thediaphragm 206 moves towards the left, in FIG. 2, air is pumped fromcavity 101 and out of port 110 into the suction housing 55, towards thecarpet. At the same time, air is drawn from the suction housing 55,along port 120 and into cavity 102. When the diaphragm 206 moves towardsthe right, air moves in the opposite direction, i.e. air is pumped fromcavity 102 and out of port 120, into the suction housing 55, towards thecarpet while, at the same time, air is drawn from the suction housing55, along port 110 and into cavity 101. At higher frequencies the phaserelationship between movement of the diaphragm 206 and movement of airthrough the port is different and typically there is a phase lag betweenmovement of the diaphragm 206 and movement of air through the port.However, at all frequencies of operation, the wave from port 110 is inanti-phase with the wave from port 120.

It will be appreciated that there is no contact between the agitationsystem and the carpet, which should have a significant benefit inreducing carpet wear. The air motion to/from the ports 110, 120 vibratesthe pile of the carpet and serves to draw out dust from between thecarpet fibres. Any dislodged dust can then be extracted with the bulkair flow, which flows into the space 55 within the suction housing,under edges 51, 52 of the sole plate or through bleed inlets on the endsof the suction housing 50.

FIG. 4 shows a single one of the cavities. The volume V of the cavity101, the cross-sectional area A of the port 110 and the length L of theport 110 determine the frequency at which this cavity/port is tuned. Theequations for this are based around the Helmholtz equation:$f_{1} = {\frac{c}{2\pi}\left\{ \frac{\pi\quad a^{2}}{V\left( {L + \frac{\pi\quad a}{2}} \right)} \right\}^{\frac{1}{2}}}$where:

-   -   c=speed of sound    -   a=port radius    -   L=port length    -   V=cavity volume

For this application we need to use the system at a point where theports 110, 120 are not tuned. Tuning the ports to a frequency that istwice that of the desired operational frequency allows a large amount ofair movement through the port. Ideally the driver box resonance shouldstill be the frequency of desired operation to maximise the Q (qualityfactor) of the system. There is a phase change on any ported systemwhere, at very low, or near zero, frequencies, the air in the port moveswith the piston. At port resonance, the port and driver are 180 degreesout of phase, both compressing and rarifying the air in the cavitysimultaneously minimising air and diaphragm excursion. At half thisfrequency (the desired operational frequency) there is a compromisewhere the air only lags behind the driver movement by a few degreesphase. The design of the driver cavity resonance should maximise theenergy in the air which is proportional to displacement (i.e. volume ofair displaced) multiplied by frequency. The actual air volume used is acompromise which allows the speaker to move enough to maintain low coiltemperatures but add enough loading so that it does not failmechanically.

This arrangement of the agitation system has some advantages. Firstly,by providing two ports 110, 120, each communicating with a respectiveside of the diaphragm 206, the diaphragm 206 is subject to an equalstatic pressure drop. This minimises, or eliminates, the tendency forthe diaphragm 206 to move towards the source of suction.

A second advantage which results from the use of two ports is noisecancellation. As the port moves air at a given frequency, pressure wavesare created into the environment making the system act as a bandpassbass reflex loudspeaker cavity. By placing the two ports close togetherthey operate out of phase, cancelling the pressure waves and thereforereducing the noise level of the system to a point which should be belowthat of the vacuum cleaner. It should be noted that the term “close”means that the distance between port centres is small compared to thewavelength of the frequency being produced. The amount of sound levelreduction depends on the symmetry of the system, i.e. the volumes of thecavities and the port sizes, the distance between the ports, the absenceof any obstructions near the port entry/exit, the frequency of theresulting wave. Also, any transmission of sound through the walls 100 ofthe cavity determines the lowest possible sound level of the system.

In this embodiment, each of the cavities 101, 102 is shown having thesame shape and volume. It is possible to vary the shape of each cavity,e.g. cavity 101 could have a lower height than cavity 102, although itis important that the volumes of the cavities should be equal, and thatthe system Q factor is as balanced as possible.

The ports 110, 120 are shown angled towards one another. Although theports 110, 120 can be vertically directed, a direction of an angle θfrom the vertical (as shown in FIG. 5) has the advantage that the airflow from the ports has both transverse and vertical components to itsvelocity. An angle θ of 90° will also work, although it works less well.

FIGS. 6 and 7 show two ways in which the driver 200 can be driven. FIG.6 shows a simple scheme in which the driver 200 is connected to a mainselectricity supply via a transformer 302. The transformer 302 serves tostep the voltage from mains voltage (240V or local equivalent) down to alower voltage, e.g. 12-50V, which is suitable for driving the driver200. In this scheme the driver 200 is driven at the frequency of themains supply, i.e. 50 Hz or 60 Hz. This scheme has the advantage ofrequiring few components, but has the limitation that the driver 200 canonly operate at the frequency of the mains supply.

FIG. 7 shows an alternative scheme where the driver 200 is driven by anamplifier 310. The amplifier 310 is powered, in a conventional manner,by a power supply (+V_(s), −V_(s)) which is derived from the mainssupply of the vacuum cleaner. An oscillator 320, or other frequencysource, is connected to the inputs of the amplifier 310. The signal fedto the driver 200 is thus an amplified version of the signal generatedby source 320. While this scheme requires more components, it offers theuser with control over the intensity of the signal generated by driver200, by control of the amplifier gain. A manual control can be providedon the cleaning head, or on the main body of the vacuum cleaner, to varythe intensity of the driver 200.

The optimum frequency of operation of the driver 200 has been found tovary according to the type of carpet. Factors such as the density andlength of fibres forming the carpet pile and the weave of the carpetdetermine the frequency at which the fibres will move. Ideally, thedriver 200 operates at the resonant frequency of the carpet. Thisrequires the driver to be variable. The circuitry shown in FIG. 7 allowsthe frequency of operation to be varied, by varying the frequency of thesignal source 320. A further manual control can be provided on thecleaning head, or on the main body of the vacuum cleaner, to vary thefrequency of the source 320. The control can be marked with thefrequency or, more helpfully, with labels indicative of the type ofcarpet which correspond to each frequency in the range. For example, afrequency of around 50 Hz could correspond to “plush carpets” and afrequency of around 115 Hz could correspond to “Wilton carpets”.

A further refinement is shown in FIG. 8. Here, the scheme of FIG. 7 hasbeen adapted so that the frequency of operation of driver 200 isautomatically determined by a carpet type detector. For convenience, thesignal which is applied to amplifier 310 is generated by amicroprocessor 340. Microprocessor 340 can generate a signal using datastored in a memory associated with the microprocessor 340. Themicroprocessor 340 also has an ultrasonic transmitter and receiverassociated with it. Under the control of microprocessor 340, transmitter342 emits a signal, with a predetermined frequency, towards the carpet.Transmitter 344 receives a signal from the carpet and either theamplitude, phase or time delay of the received signal with respect tothe transmitted signal, or a combination of these quantities, can beused to determine the type of carpet.

The analysis of the received signal is performed by the microprocessor340 and used to determine which one of the stored signals should beapplied to amplifier 310. It will be appreciated that other techniquescould be used to determine the carpet type, such as the use ofelectromagnetic radiation of a predetermined frequency, or band offrequencies.

For completeness, FIG. 17 shows a cylinder type of vacuum cleaner(called a canister or barrel cleaner in some countries) with a floortool 40 incorporating the agitation apparatus.

So far, the driver 200 has been shown as a diaphragm with the driver(magnet, coil etc.) positioned in one of the cavities 101, 102. Thepresence of the driver in one of the cavities should not significantlyaffect the symmetrical nature of the system, since air can easily reachthe diaphragm 206 by passing through and/or around the structure of thedriver. Referring again to FIG. 3, the suspension 212 of the driver isporous and there are spaces in the chassis 208. However, it ispreferable to increase the size of cavity 102 compared to cavity 101 sothat the free-space, volume of cavity 102 matches that of cavity 101,i.e. the total volume of cavity 102 equals the volume of cavity 101 plusthe volume occupied by driver 200.

In an alternative scheme the driver itself is symmetrical. As shown inFIG. 9, this has the structure of two drivers 200, 200′ mounted face onto one another, with the diaphragm 206 being common to both drivers.Connections to the coils 215 of the drivers are reversed with respect toone another so that the drivers serve to drive the diaphragm 206 in thesame direction when they are energised by a common signal. To explain,driver 200 moves diaphragm 206 towards the left at the same time asdriver 200′ also moves diaphragm 206 towards the left. Diaphragm 206 canbe a single diaphragm or it can be two diaphragms mounted face-to-facewith one another.

In a further alternative scheme, shown in FIG. 10, each cavity has onecomplete driver unit 200 mounted within it, with its own diaphragmformed in the wall with the neighbouring cavity. Connections to thecoils of the two drivers 200 are reversed so that the two drivers bothmove their respective diaphragms in the same direction.

The driver or drivers do not have to be positioned within the resonantcavities 101, 102, nor do they need to be positioned directly above thecleaning head. In the embodiment shown in FIGS. 11-13 the driver (ordrivers) 200 are mounted within small cavities 501, 502 positionedremotely from the resonating cavities 503, 504 and a pair of connectingpipes 505, 506 join the cavities 501, 502 to resonating cavities 503,504. By using a small driver cavity and maximising the pressureavailable at the connecting tubes, a second cavity can be used for theport/cavity resonance. The remote mounting of the driver has theadvantages of reducing the size of the cleaner head and allows a greaterchoice of driver, since there is less restriction on dimensions etc.

The remote positioning of the driver 200 can have a penalty in a slightloss of performance, since there are losses which result fromtransmitting pressure waves down the connecting pipes 505, 506. As arule, these losses tend to increase as the connecting pipes 505, 506 aremade narrower and longer. We believe that these losses can be minimisedif the connecting pipes 505,506 have a cross-sectional area which istwice that of the ports 510, 520, and if the pipes 505, 506 are keptreasonably short. The system needs to be tuned to avoid the internalcavity absorbing the resonance of the external cavity (and hencereducing the energy available.) In this case, the driver cavityresonance should be twice that of the port cavity resonance and hencethe upper section is ‘stiffer’ than the lower section, keeping thesystem Q factor high to maximise energy available at the end of theconnecting pipes 505, 506.

FIG. 12 shows one way in which this remote positioning of the driverscan be implemented in an upright type of vacuum cleaner, with thedrivers 200 housed at the base of the upright part of the main body 530of the vacuum cleaner. FIG. 13 shows one way in which the drivers 200can be remotely housed on a cylinder type of vacuum cleaner, the drivers200 and driver cavities being mounted to the wand 550 of the vacuumcleaner.

While it is possible to provide a cleaning head with a single pair ofcavities, it is preferred to employ an array of such devices in orderthat a good level of agitation is delivered across the entire width ofthe cleaning head. FIG. 14 shows a scheme with multiple sets ofcavities. Each pair of cavities 410, 420, 430, 440, 450 are positionedfront-to-back and aligned next to one another across the width of thecleaning head. For clarity, axis 401 indicates the longitudinal axis ofthe cleaning head and axis 402 represents front-to-back.

In an alternative scheme, each pair of cavities can be aligned with thelongitudinal axis 401 of the cleaning head. FIG. 15 shows across-section along the longitudinal axis of a cleaning head in whichthe cavities are mounted in this way. The gaps between the ports shouldnot degrade performance as there is significant air movement either sideof the ports.

In a still further alternative scheme, each cavity can have multipleports which connect the interior of the cavity with the suction housing.The driver should be appropriately matched to the volume of the cavity,the cross-sectional area of the ports and thus the amount of air whichit is expected to move.

In the driver shown in FIGS. 2 and 3 the magnet 210 is stationary whilethe coil 215 is movable with the diaphragm. In an alternative form ofdriver, shown in FIG. 16, the driver has a fixed coil 225 and a movablemagnet 220. Air movement through the ports 110, 120 can be used to coolthe driver. Magnet 220 is in the form of a ring magnet which fits arounda magnet former 221. A cavity 228 in the cup 203 at the rear of thedriver houses a heat conducting fluid or gel and a heatsink is mountedon the rear of the pole plate. This should allow good cooling when thedriver is driven hard since the air entering the port naturally passesthe heatsink fins 230. This design may be preferable to a moving coildevice in which the motion of the driver cools the coil by a bleedthrough the suspension. This also will allow a driver to be used with asealed coil to prevent dust ingress.

In each of the embodiments described above, the driver has been aloudspeaker type of assembly driven by an ac source. However, thediaphragm can be moved in other ways, such as by a motor-driven piston.The frequency at which the diaphragm is moved can be in the same rangeas for the loudspeaker embodiments, and the control of the frequency ofthe diaphragm can be controlled by control of the motor speed. In thescheme shown in FIG. 18 a housing 100 has two cavities 101, 102 withports 110, 120, as before. Two diaphragms 261, 262 are positioned withinthe housing 100 and are connected to the wall of the housing 100 by acombined suspension and seal 255, 256. A cam 250 is mounted between thediaphragms 261, 262, the cam 250 being eccentrically mounted about aspindle 252. The spindle is driven by a motor via a direct or indirect(geared) coupling. The two diaphragms 261, 262 lie against the cam 250at all times and thus the position of the diaphragms 261, 262 withintheir respective cavities 101, 102 is always controlled by the positionof the cam 250. As cam 250 rotates, diaphragms 261, 262 move about arest position. During one half of the cycle of the cam 250, diaphragm261 moves towards the left, reducing the volume of cavity 101, whilediaphragm 262 moves towards the left, increasing the volume of cavity102. During the other half of the cycle of cam 250, diaphragm 261 movestowards the right, increasing the volume of cavity 101, while diaphragm262 moves towards the right, decreasing the volume of cavity 102.Movement of the diaphragms 261, 262 generates a pressure wave in thesame manner as the loudspeaker embodiments.

While it is convenient to power the driver via an electrical supplywhich is derived from a mains supply, it is also possible to power thedriver by a turbine which is powered by air flow through the vacuumcleaner. The turbine can be positioned in the main airflow path throughthe machine—a so-called ‘dirty air’ turbine—or it can be positioned in aseparate, clean air, airflow path into the machine. In FIG. 18 thespindle 252 which drives cam 250 can be coupled to a turbine via ageared connection. Knowing the normal airflow rates through a vacuumcleaner in which this is to be used, appropriate gearing can be providedbetween the turbine and the cam 250 so that the rate of rotation of thecam 250 is in the range required to agitate the floor surface.

1. An agitation apparatus for a cleaning appliance comprising a wavegenerator configured for generating alternating pressure waves, a firstfluid flow path with a first inlet/outlet port and a second fluid flowpath with a second inlet/outlet port, the area adjacent first and secondthe inlet/outlet ports forming an agitation region, wherein the wavegenerator is arranged to generate a first alternating pressure wavealong the first fluid flow path and a second alternating pressure wavealong the second fluid flow path, the first and second pressure wavesbeing substantially in an anti-phase relationship with one another. 2.An agitation apparatus according to claim 1 wherein each flow pathcomprises a cavity.
 3. An agitation apparatus according to claim 2wherein the cavity is a resonating cavity.
 4. An agitation apparatusaccording to claim 2 wherein the cavity in each flow path is of the samevolume.
 5. An agitation apparatus according to claim 1, 2, 3 or 4wherein the cavity is directly adjacent to the wave generator.
 6. Anagitation apparatus according to any one of claims 2 to 4 wherein eachof the flow paths includes a cavity with a port extending directly fromit.
 7. An agitation apparatus according to claim 1, 2, 3 or 4 whereinthe cavity is located away from the wave generator and is joined to thewave generator by a duct.
 8. An agitation apparatus according to claim1, 2, 3 or 4 wherein the wave generator comprises a diaphragm, a firstside of the diaphragm communicating with the first flow path and asecond side of the diaphragm communicating with the second flow pathwhereby to generate the first and second alternating pressure waves. 9.An agitation apparatus according to claim 8 wherein the wave generatorfurther comprises a driver for driving the diaphragm and wherein thedriver is housed within one of the flow paths.
 10. An agitationapparatus according to claim 8 wherein the wave generator furthercomprises two drivers for driving the diaphragm, and wherein the driversare mounted on each side of the diaphragm, a first of the drivers beinghoused in the first flow path and a second of the drivers being housedwithin the second flow path.
 11. An agitation apparatus according toclaim 1, 2, 3 or 4 wherein the wave generator comprises two diaphragms,a first of the diaphragms communicating with the first flow path and thesecond of the diaphragms communicating with the second flow path, and adriver for driving the diaphragms which is positioned between thediaphragms.
 12. An agitation apparatus according to claim 1, 2, 3 or 4wherein the wave generator comprise a coil and a magnet, one of the coilor magnet being movable with respect to the other, the coil receiving analternating signal for energizing the coil.
 13. An agitation apparatusaccording to claim 12 wherein the coil receives a signal at thefrequency of the mains supply.
 14. An agitation apparatus according toclaim 12 further comprising a signal source for generating analternating signal for supplying to the coil.
 15. An agitation apparatusaccording to claim 12 wherein the wave generator comprises aloudspeaker.
 16. An agitation apparatus according to claim 1, 2, 3 or4wherein the wave generator is driven by airflow.
 17. An agitationapparatus according to claim 16 further comprising a turbine forpositioning in an airflow path to the vacuum cleaner and a coupling forcoupling the output of the turbine to the wave generator.
 18. Anagitation apparatus according to claim 1, 2, 3 or 4 wherein the wavegenerator generates a pressure wave with a frequency in the range 0-200Hz.
 19. An agitation apparatus according to claim 18 wherein thefrequency of operation of the wave generator is variable.
 20. Anagitation apparatus according to claim 19 wherein the frequency of thewave generator is manually adjustable by a user of the apparatus.
 21. Anagitation apparatus according to claim 19 further comprising a detectorfor detecting the type of floor surface and wherein the frequency ofoperation of the wave generator is variable according to the detectedtype of floor surface.
 22. A cleaning head comprising a housing having asole plate for travelling across a surface and an agitation apparatusaccording to claim 1, 2, 3 or
 4. 23. A cleaning head according to claim22 in the form of a cleaning head for a vacuum cleaner, wherein thehousing is a suction housing having a suction outlet for connecting to asource of suction and the ports of the agitation apparatus are spacedapart along the housing.
 24. A cleaning head according to claim 22wherein the ports are directed downwardly towards the sole plate.
 25. Acleaning head according to claim 22 wherein the ports are inclined withrespect to the sole plate of the cleaning head.
 26. A cleaning headaccording to claim 22, comprising a plurality of the agitationapparatus.
 27. A cleaning head according to claim 26 wherein theagitation apparatus are spaced along the longitudinal axis of thecleaning head.
 28. A cleaning head according to claim 22 in the form ofa tool for fitting to a wand.
 29. A vacuum cleaner comprising a mainbody and a cleaning head, wherein part of the agitation apparatusaccording to claim 21 is housed in or on the main body of the vacuumcleaner and ducting connects the part of the agitation apparatus in oron the main body to that part of the agitation apparatus on the cleaninghead.
 30. An agitation apparatus as claimed in claim 21 for use with avacuum cleaner having a cleaning head, wherein the inlet/outlet portsjoin the flow paths to the space within the cleaning head. 31.(canceled)
 32. A vacuum cleaner comprising a main body and the cleaninghead according to claim 26, wherein part of the agitation apparatus ishoused in or on the main body of the vacuum cleaner and ducting connectsthe part of the agitation apparatus in or on the main body to that partof the agitation apparatus on the cleaning head.